The present invention relates to polyolefin-based resin compositions reinforced with filler and to automotive molded plastics made from the resin compositions, such as automotive garnish or trim members, which are disposed in the interior (i.e., passenger compartment) of an automobile, for covering pillars and side roof rails of the automobile. With the use of such plastics, the automobile interior is improved in appearance.
Conventional automotive molded plastics by themselves which are made from conventional polyolefin-based resin compositions are not sufficient in scratch resistance. Some of these plastics are improved in scratch resistance by increasing hardness thereof. They are, however, still not sufficient in scratch resistance. In other words, they have a sufficient resistance to weak scratching caused, for example, by rubbing of cloth, by fingernails, and by other members, but still have an insufficient resistance to strong scratching caused by a sharply cornered object. Thus, conventional automotive molded plastics used, for example, as pillar garnish member (i.e., garnish for covering automotive pillars) may have scratches by a strong impact, for example, of the tongue portion of an automotive seat belt. In FIG. 3, there is shown an automotive pillar garnish member 10 for covering an automotive front pillar 12. This pillar garnish member 10 is made from a thermoplastic resin and has conventional reinforcing ribs 14. The automotive pillar garnish member 10 is required to have characteristics of decoration, stoutness, high rigidity, high quality, and the like. In particular, it is required to have high rigidity at the time of its installation in automobile and at high temperature and high moldability. A thermoplastic resin reinforced with filler (e.g., talc) has good characteristics such as high moldability. An automotive pillar garnish member made from this resin is, however, still insufficient in scratch resistance.
Some of conventional molded plastics, such as plastics used as automotive bumpers, are prepared by adding elastomers to the other components thereof. Such plastics are, however, insufficient in elastic modulus for the use, for example, as pillar garnish member.
It is therefore an object of the present invention to provide a polyolefin-based resin composition that is capable of providing a molded plastic article which is substantially improved in scratch resistance, while the molded plastic has good characteristics, such as high rigidity, which are comparable to those of conventional pillar garnish members.
It is another object of the present invention to provide such molded plastic article.
According to the present invention, there is provided a polyolefin-based resin composition that is in an amount of 100 wt % in total, said composition comprising:
(a) 60-66 wt % of a crystalline propylene-ethylene block copolymer, said block copolymer comprising a first segment of a homopolymer of propylene and a second segment of a copolymer of propylene and ethylene, said block copolymer having an isotactic pentad tacticity of at least 0.96, a ratio of a weight average molecular weight of said block copolymer to a number average molecular weight of said block copolymer being not greater than 6;
(b) 12-20 wt % of an ethylene-propylene copolymer rubber containing therein 50-60 wt % of ethylene, said rubber having a Mooney viscosity of from 45 to 55 at 125xc2x0 C.;
(c) 18-25 wt % of an inorganic filler that is one selected from the group consisting of a talc, a first combination of said talc and a glass fiber, and a second combination of said talc and a whisker, said talc having an average particle diameter of not greater than 2 xcexcm, said glass fiber having an average fiber length of from 5 to 10 mm and an average diameter of from 15 to 20 xcexcm, and said whisker having an average fiber length of from 15 to 25 xcexcm and an average diameter of from 0.5 to 1 xcexcm.
According to the present invention, there is further provided a molded plastic article made from the above polyolefin-based resin composition.
A polyolefin-based resin composition according to the present invention is capable of producing a molded plastic article which is particularly improved in scratch resistance (i.e., resistance to scratching). In other words, a molded plastic article according to the present invention hardly receives substantial damage (e.g., scratches, cuts, marks, and the like) thereon, even if a sharply cornered object (e.g., the tongue portion of an automotive seat belt) hits strongly against the molded plastic article. In the invention, the molded plastic article is provided with good elasticity by the incorporation of the above particular amount of the special copolymer rubber. With this, the molded plastic article is substantially improved in scratch resistance. Furthermore, the inventors have unexpectedly found that Izod impact value of a molded plastic article is an effective parameter for evaluating scratch resistance thereof.